The objective is to explore the role of histoblood group antigens in virus-induced asthma exacerbations. These antigens (ABH and Lewis) decorate O- and N-linked glycans on mucin and epithelial glycoproteins, respectively. Glycan synthesis involves glycosyltransferases, including fucosyltransferases encoded by FUT genes; glycan degradation involves glycosidases, including fucosidase. "Secretor status" is defined by FUT2 activity in epithelial cells, which forms the H antigen and allows subsequent synthesis and secretion of A, B, and Lewis B antigens. In preliminary data, we found that asthmatic subjects with frequent exacerbations are more likely than non-exacerbators to be secretors, that secretors more frequently report that a cold causes asthma, and that sputum in stable asthma has abnormally high fucosidase activity. This suggests that airway glycans are subjected to 2 competing homoeostatic influences, a) the diversity and activity of glycosyltransferases within cells that synthesize glycans, and b) the diversity and activity of glycosidases that turn over and remodel them in the airway lumen. We hypothesize that secretor positive asthmatic subjects are susceptible to virus-induced asthma exacerbation and that abnormal glycosidase activity in secretions modifies the glycan coat and promotes virus-induced exacerbation. In Aim 1, we propose a case control study to compare secretor status in hospitalized asthmatics and outpatient asthmatics without a history of exacerbation. The relationships between secretor status and FUT gene and histo-blood group antigen expression in airway epithelial cells will also be established. In Aims 2 and 3, we will determine if binding of rhinovirus to airway mucins or to airway epithelial cells is influenced by secretor status or by fucosidase activity. In Aim 4 we will determine if Th2 cytokines influence epithelial cell susceptibility to rhinovirus infection by changing epithelial cell expression of glycolytransferases or glycosidases. These are novel lines of inquiry into the mechanisms of virus-induced asthma exacerbation and may prompt novel treatments.